Ozone produced in photochemical smog poses a significant health risk in the Los Angeles Basin. A complete understanding of the chemistry involved in ozone formation is required in order to formulate proper regulations of chemical emissions that are most effective in reducing the smog problem. Peroxy radicals are precursors in the formation of tropospheric ozone via reaction with NO and NO2. Rate coefficients for these reactions for hydrocarbons larger than ethane have not been measured. In this study, rate coefficients for the reaction of alkyl peroxy radicals deriving from C3 -Ce alkanes with NO, NO2, and their self-reaction will be measured using a technique of pulsed infrared laser thermal lens spectrometry to monitor the peroxy radical concentration as a function of time. The gas mixture composition is adjusted in order to isolate specific ROO product channel reactions. A vibrational mode of ROO is excited with a pulsed CO2 laser, and the thermal gradient resulting from the release of energy to translational degrees-of-freedom is probed with a cw HeNe laser. The change in intensity of the HeNe laser as the thermal gradient forms is monitored by a photodiode. The magnitude of the thermal lens signal is proportional to the ROO concentration. By varying the time delay between the flashlamp and the CO2 laser pulses, the kinetic information for removal of ROO will be determined. Rate parameters will be obtained by fitting the raw data to a complete reaction mechanism using least-squares techniques. From this analysis scheme, rate coefficients will be determined for reactions of peroxy radical with NO and NO2 as well as the ROO self-reaction.